For example, GB 2 391 907 A (JP-A-2004-060525) discloses an integrated valve device provided in an intake manifold of an internal combustion engine. The integrated valve device includes multiple valves connected via one shaft. Alternatively, for example, U.S. Pat. No. 6,979,130 B1 (JP-A-2003-509634) discloses an integrated valve device provided in an intake manifold of an internal combustion engine. The integrated valve device includes multiple valve units axially connected to define a predetermined distance adjacently therebetween. Each of the valve units includes one resin housing and one resin valve. Each resin valve is, for example, a butterfly valve having a plate-shaped valve members radially extending from the valve shaft toward radially both ends.
In such an integrated valve device, multiple valves are provided in intake passages of an intake manifold of an engine, and are arranged along a shaft (pin rod). The pin rod, which is a singular component, may be press-inserted into through holes of the valves, so that the valves are skewed with the pin rod. In this insertion, the valves may be axially biased to one side due to friction between the inner periphery defining the through hole and the outer periphery of the pin rod, and consequently, the valves may be eccentrically displaced in the intake passages.
In this condition, the clearances between the valves and the intake passages become nonuniform due to the eccentrically displacement of the valves. Consequently, leakage of intake air flows passing through the left and right side clearances become nonuniform when the valves are in a full close position to define a minimum opening in the intake passages. As a result, engine performance is lowered.